Process of dehydrating caustic



NBV. s, 1929. J. F. WAIT 1,734,699

PROCESS OF DEHYDRATING CAUSTIC Filed Dec. 31, B24

W cf W, INVENTOR %TTORNEY Patented Now. a, 1929 JUSTIN I. WAIT, 0! NEW YORK, N. Y., ASSIGNOB '10 NATTONAL d:

. 00., INOQA CORPORATION 01 NEW YORK v I Gammon.

PROCESS OF DEHYDR ATI NG CAUSE-IO Application 11.1mm. a1, 1924. serial No. 759,046.

This invention relates to a process and apparatus for dehydrating materials. It is especially applicable to dehydrating such materials as caustic, for example, where it is desirable to reduce the water content to as low as 10% or less.

Heretofore in dehydrating materials of this character, the materials have been placed in a closed vessel to the outside of which heat was applied for raising the temperature and a vacuum was also sometimes maintained to facilitate the o eration. In such dehydration processes ifficulties and troubles often "arose because the material was subject to foaming and was a t to foam over if the vacuum was too hig or if heat was -ap lied too rapidly with consequent losses an interruption .of the process. Because of the danger of foaming over the operation was often carried out with very much less material in the vessel than was possible so as to minimize these dangers. In such cases the volume of the material often became very small and caused local overheating and consequent de-' struction of the dehydrator.

When caustic materials are bein dehyrated' visual inspection of the interior of the dehydrator is not practicable during the pro without necessitating an inspection of the inside of the dehydrator. Provision is also made for maintaining a vacuum, carrying away and condensing vapors, and means may be provided for observing the amount of vapors, beingcondensed at any particular time, 7

An arrangement of apparatus suitable for carrying out the process-is illustrated in the accompanying drawings in which reference character 1 indicates a closed metallic vessel or dehydrator which may be heated from any convenient source 2. The dehydrator is provided with a valved feed pipe 3 and an outlet pipe 4 which leads'to a condenser 5 that is 111 turn connected to a separator 6 which may be connected to any convenient means 7 for producing a vacuum. A sight glass 8 may be inter osed in the line between the condenser 5 an the separator 6for enabling the condensate to be observed.

The dehydrator 1 may be provided with a valved pipe 9 reaching below a point at which it is deslred to maintain the liquid level. The ipe 9 leads from a source of gas supply not-s own and-has an orifice and a manometer 11 for indicating the quantity of gas flow. Another manometer. 12 is provided to indicate the pressure in the pipe 9. The readings of the two manometers can be calibrated to show the liquid 'level, in the dehydrator 1 when gas is passed through the pipe 9 intothe liquid. Other means may be used for indicating the liquid level without visual or physical access to the vessel 1. The dehydrator 1 also hasan electrode 13 projecting through an insulated air-tight hole 13' in the cover to a distance above which the foam from the materials being deh drated drator 1, being grounded. The dehydrator may also be provided with a thermometer 17 and a large ipe 18 leading to a lace of safet This pipe 18 may be provi ed with a sa ety blank 19 which will be ruptured as soon as the pressure reaches a predetermined limit. A valved discharge pipe 20 leads to the bottom of the dehydratorl and may be used for discharging the dehydrated contents.

The 0 eration is as follows: The material to be de iydrated is introduced through the inlet pipe 3 into'the dehydrator 1 until the desired level'is reached, and heat is applied to increase the temperature to the point at which vapors pass off. IBy inject ng gas v through the pipe. 9, the readings of the manometers 11 an'd'12 will indicate the depth of liquid in the dehydrator and if foam risesuntil it contacts with the lower end of the electrode 13, a circuit will be completed through the wall of the deb drator 1, the foam, electrode 13, alarm 14, attery 16 and theground, thus giving a Warning. The

operating conditions can then be regulated as, for example, by decreasing the vacuum or alterin the rate of feed or reducing the rate 'of app yin" the heat.

- caustics is introduced into the dehydrator 1 until a. level approximating at least of the volume of the vessel is reached and heat is applied. Pressure is maintained below 12 pounds absolute. As evaporation takes place and the volume of the boiling mass decreases, additional liquid is fed to maintain the desired liquid level. The rate of heating is such as to avoid excessive foaming of the contents of the vessel. If excessive foaming should occur, the foam would'contact with the 350 C. is passed to prevent foaming over,

electrode 13 causing an alarm whereupon the rate of firing or other conditions may be altered to reduce the foam level. Thereafter the weak liquid is fed in continuously, usual- 1y with noticeable rise in the boiling point of' the mass, the feed being dependent somewhat upon the vacuum maintained upon the system. It-is usually desirable to maintain a temperature between 200 and 300 C. while thus feeding the liquid, the higher temperature usuall v existing toward the end of the feed. After this approximate temperature has been reached the feed is stopped and the temperature further increased to above 400 (1, cantion being taken as the temperature of about which is most apt to occur at or near this temperature. At a somewhat higher temperature the heating rate may be again increased until the final temperature is reached. This temperature in turn depends upon the vacuum maintained and the final degree of dehydration desired. It has been found that with a final temperature of about 470 and a v'aeuum corresponding to about 2 pounds absolute pressure, a deb drated caustic containing less than 1%. o .moisture is produced. This is usually suitable for commercial use. v

? During the operation it is desirable to condense and recover-the vapors since they contain an appreciable quantity ofcanstie,

entrained or otherwise carrie therewith. This is true in particular when the dehydrator is being forced to obtain a high output which 1 400 C. while maintaining the vapor be suddenly released to cause a posithe pressure on the dehydrator, it may be reduced by means of the safety blank 18 and the foamand vapors therefrom may be diverted away from t 1e operating space.

When the charge has been completedit is withdrawn by applying slight pressure to the dehydrator or vacuum to a receiver attached to pipe 20. For other kinds of caustic and for extending the life of the equipment with the mixture of sodium and potassium hydroxides, it isdesirable to reduce the operation temperature materially below the 47 0 C. suggested above. This is made possible by car- I rying out the dehydration under an unusually high vacuum of less than 1 pound absolute pressure. Under these conditions the'final temperature required for a desired degree of dehydration is materially less. In order to avoid overheating of the metallic vessel and to obtain uniform extraction of heat by the liquid, the level of liquid insidefhe vessel should not be permitted to vary more than about 20% from the level at which. the operation has been found to be most satisfactory.

' Among the-advantages to be gained by this method of operation involving specific control of the liquid level within the dehydrator are increased safety of operation, increased capacityand increased life of equipment.

I claim:

l. The process of dehydrating caustic alkali containing in excess of 10% moisture;

which comprises introducing the caustic into a closed vessel until approximately 40% of the volume of the vessel is filled, heating the vessel while maintaining the pressure in said vessel below 12 lbs. absolute, introducing I weak caustic liquor into said vessel while maintaining the temperature of the liquor in said vessel between 200 and 300 0., discontinuing the introduction of weakcaustic liquor into said vessel and raising the tem--. perature of theliquor in said vessel to above pressure in said vessel at about 2 lbs. absolute.

2. The process of dehydrating caustic alkali which comprises introducing the causticinto a vessel, heating the vessel while maintaining thepressure in said vessel at a low vacuum, introducing weak caustic liquor into said vessel while maintaining the temperature of the liquor in saidvessel between 200 and 300 G.,' discontinuing the introduction of weak causticinto said'vessel and raising the temperature ofithe liquor in said vessel to above 400? Oiwhile maintaining the pressure in said vessel at a-high vacuum. I

v In testimony whereof l aflix m 'sigm'tuie. A JUSTIN. F. WAIT. 

